Maintenence from Husband

I'm looking to be guided on my Sister ( a Home maker ) married for over 24 years with 2 grown-up children studying post graduation, one of them in premium University for MBA near Delhi. Despite several constraints she was advised to be contended within the family even tough the Husband had been influenced badly earlier by her Mother in law, and now by Brother & Sister in Law. The Husband along with 2 year elder brother ( married with 2 children and staying in an independent house ) runs a joint business of Freight Forwarding & owns a fleet of Trucks for over 40 years. They have an indicative Monthly Income of well over 5 Lakhs & more with rentals from several Properties. The properties are owned jointly, as it happens to reduce the Tax burden, with ownership with my Sister, Husband, Brother, Brother' Wife, etc., etc., which together can be valued at more then 20 crores. In a way my Sister & 2 kids are only there for a formality & husband only for ornamental reason, neither as a husband & nor a father. The kids have been most hurt & frustrated as they are fully grown up at 23 & 21 and are furious at the state of affairs & the way they are treated. My Sister is given Rs 20,000 monthly for expenses, sometimes not, which are just not good enough to meet even the Expenditure of upkeep of her & the kids and their basic maintenance. The situation is getting worse day be day even though she cooks for him & the family. In fact my Sister, on & off, has had to be treated for mental stress at Home & on the Depression drugs and we had to bring her to our Home for sort of rehabilitation. I would seek help & guidance from all leaned lawyers if she ( & Kids who are major ) can take any legal recourse on seeking Maintenance Allowance and the process thereof. Appreciate all possible path(s) to pave a way for good. Please get back on any more information you may need to provide a short & long term Solution.